1. Field of the Invention
The present invention relates to devices that measure the motion of one human body part relative to another. In particular, the present invention relates to an apparatus for measuring the range of angular body motion about at least one axis of rotation.
2. Description of the Prior Art
Measuring the motion of a portion of a human body relative to another has been done utilizing compass-type angle indicators and pendulum-type inclinometers. Caliper-type devices, such as a spondylometer, used in combination with a protractor, also have been used to measure the motion of the thoracic and lumbar spine relative to the sacrum. However, the development of devices which are removably and stably mountable to the spine or other human body parts, and that do not require any repositioning of the device during the measurement process, while yielding accurate, verifiable, and reproducible data has not been accomplished by the prior art.
U.S. Pat. No. 2,532,915 discloses a device for determining the relative displacement of vertebrae through auditory signal analysis. The device uses a compass and a bubble level to orient the device and applies auditory signals to be transmitted through the vertebrae column and received by sound receivers.
U.S. Pat. Nos. 3,921,620, 3,943,912, and 4,587,956 disclose devices which comprise a magnetic body attached to a belt which is wrappable about the human torso or other body limb. The devices provide a magnetic field which is used to apply a magnetic flux to the human body for therapeutic purposes.
U.S. Pat. No. 4,108,164 discloses a device that measures flexural movement of the human torso. The device has a jacket with an angle sensing means, whose output is sensed by an electrical measurement device and which measures the angle of tilt of portions of the spine during the human act of leaning. U.S. Pat. No. 4,444,204 discloses a device for measuring scoliosis. The device is comprised of a frame with several laterally spaced parallel finger-like members situated to mimic the lateral curvature of the spine.
U.S. Pat. No. 4,485,825 discloses an instrument for measuring the positions and relative displacements of portions of the human body, including joints and the spinal column. The device uses a belt or suction cup to mount the instrument to the human body. The instrument includes a pendulum-type inclinometer and a compass-type angle indicator. To measure the motion of a body part relative to another, one instrument is placed on each of the cooperable body parts. Then compass and inclinometer readings are taken from each instrument before and after a controlled movement of a body part. The data is compared to measure the relative displacement of body parts. The device is also capable of measuring rotation of the spinal column by manipulating the compass device to a horizontal plane. This instrument is usable in a range of motion measurement method, such as the two inclinometer technique as disclosed in an article by Mayer et al., in SPINE, Vol. 9, No. 6, 1984.
U.S. Pat. No. 4,655,227 discloses a device used to determine mechanical injuries of the spine. The device is comprised of a computerized system whereby a mathematical model of a spine applicable to the five lumbar vertebrae and their respective structures, is compared to the actual movement of the spine measured by the use of a camera and an associated computer program.
U.S. Pat. No. 4,665,928 discloses a device used to measure the range of motion of multiple body parts relative to one another. The device is comprised of several pendulum-type electronic goniometers which are mounted to belts circumferentially wrappable about a human body part. The measurement output of the goniometers is read by a computer, which analyzes and compares the relative readings of the goniometers to determine the range of motion for a body part relative to another.
U.S. Pat. No. 4,730,625 discloses a device for monitoring the posture of a human and includes a shirt worn by the subject with an electronic sensor connected to a resistive element on the shirt. Upon a change in posture, the resistance of the element changes and the sensor indicates that a change in posture has occurred.
U.S. Pat. No. 4,777,965 discloses a device for measuring the range of motion for the cervical spine about three axis of rotation. The device utilizes a common eye- glass frame releasably securable on a human subject by means of nose pads and ear pieces. The device includes a pendulum-type angle finder situated about a horizontal axis and a compass-type angle finder situated about a vertical axis such that the two angle finders are mutually perpendicular to each other. The pendulum-type angle finder and compass are rotatable 90 degrees to permit tri-planar angle measurements of the cervical spine.
U.S. Pat. No. 4,839,809 discloses a device for measuring human ambulatory turning behavior. The device includes a compass means which generate electronic signals thereby indicating the degree and direction of ambulatory rotational movement of the subject.
Thus, the use of compass-type devices, pendulum-type devices, and caliper-type devices have been used to measure the motion of one body part relative to another. In particular, spinal range of motion has been measured for flexion and extension relative to the sacrum, as well as lateral bending and rotation of the spine in the pelvic area.
However, these devices generate a variety of errors within the measurement method. For example, in spinal measurements the inclinometer-type device may rock on the sacrum or on measurement points located on the human torso. Likewise, if the single inclinometer technique is used, then the inclinometer must be repositioned several times to measure range of motion for both flexion and extension. This repositioning introduces measurement errors because of shifting reference points. Another significant problem is relocating the prior measurement point or location on a human torso if a range of motion test is desired to be replicated at a subsequent testing period. The single or double inclinometer technique also presents difficulties in distinguishing pelvic motion from torso motion. Rotation measurements of the torso using a singular compass-type device also have been plagued with measurement errors because it is difficult to isolate true torso rotation from unwanted pelvic rotation.
There is a continuing need for an improved device measuring the range of motion for body parts. The device should be designed in such a manner that it is removably mountable to the spine or body part in a stable fashion to minimize rocking of the device on the measurement locations, thereby permitting the measurement of reproducible and verifiable data. The device should be of a simple, lightweight, mechanical design.